Humidity under basking lamps
These graphs illustrate the dramatic reduction in ambient humidity
experienced directly beneath various common reptile basking lamps.
In all cases
humidity is reduced very rapidly after the lamp is turned on.
Typical room ambient humidity levels were employed as a starting
position. The general
room ambient was also monitored simultaneously at a distance of 2M
using an independent data logger.
In this first graph ambient room humidity level was 70%. Within
seconds, under the basking lamp the levels fell to 30%, then to
The lamp was switched off and levels recovered.
It was then turned on again and levels fell as before. Levels
of 20% and below are extremely damaging if sustained, even for arid
These are the effects of a 60w basking lamp (as frequently used with
hatchlings) at 30cm above the substrate.
The first is measured directly under the lamp, in the centre.
Starting humidity (background ambient) was 41%. The lamp was tuned
on at 11.00 am and off at 1.20 pm.
The minimum RH attained was 14.83%
The second graph shows the effect at 10cm from the edge of the lamp,
also at substrate level. Times are identical as both recordings were
The minimum RH attained was 19%.
Both of these levels are extremely low and sustained levels like
this would without doubt contribute to a state of chronic
dehydration and high rates of fluid loss, even in a 'desert'
One consequence. Bladder 'stones' as seen here. History: tortoise
purchased from pet shop and maintained in terrarium with overhead
100w basking lamp. Fresh water available at all times.
For comparison, this is what actually happens in the wild, during
the very hottest and driest part of the year.
Measured this last August (the hottest, driest August on record for
100 years with T. graeca graeca).
These measurements were obtained from an attached logger in direct
contact with an estivating tortoise.